1. Field of the Disclosure
The present disclosure relates generally to electrophotographic image forming devices, and more particularly to an overcoat layer for an organic photoconductor drum having excellent abrasion resistance and electrical properties.
2. Description of the Related Art
Organic photoconductor drums have generally replaced inorganic photoconductor drums in electrophotographic image forming device including copiers, facsimiles and laser printers due to their performance and advantages. These advantages include improved optical properties such as having a wide range of light absorbing wavelengths, improved electrical properties such as having high sensitivity and stable chargeability, availability of materials, good manufacturability, low cost, and low toxicity.
While the performance and advantages offered by organic photoconductor drums are significant, inorganic photoconductor drums offer much higher durability. Inorganic photoconductor drums (e.g., amorphous silicon photoconductor drums) are ceramic-based, thus being extremely hard and abrasion resistant. The surface of organic photoconductor drums is typically comprised of a low molecular weight charge transport material, and an inert polymeric binder. Therefore, the failure mechanism for organic photoconductor drums typically arises from mechanical abrasion of the surface layer due to repeated use. Abrasion of photoconductor drum surface may arise from its interaction with print media (e.g. paper), paper dust, or other components of the electrophotographic image forming device.
The abrasion of photoconductor drum surface degrades its electrical properties, such as sensitivity and charging properties. Electrical degradation results in poor image quality, such as lower optical density, and background fouling. When a photoconductor drum is locally abraded, images often have black toner bands due to the inability to hold charge in the thinner regions. This black banding often marks the end of the life of the photoconductor drum.
Increasing the life of the photoconductor drum will allow the photoconductor drum to become a permanent part of the electrophotographic image forming device. In other words, the photoconductor drum will no longer be a replaceable unit nor be viewed as a consumable. Photoconductor drums with a life-of-the-printer will allow the printer to operate with lower cost-per-page, more stable image quality, and less waste.
To achieve a long life photoconductor drum, especially with organic photoconductor drum, a protective overcoat layer may be coated onto the surface of the photoconductor drum. An overcoat layer formed from a crosslinkable silicon material has been known to improve life of the photoconductor drums used for color printers. However, such overcoat layer does not have the robustness for edge wear of photoconductor drums used in mono printers. A photoreceptor overcoat comprising a UV crosslinked layer of hexacoordinate urethane acrylate and UV crosslinkable charge transport molecule is disclosed in U.S. patent application Ser. No. 13/731,594 entitled “PHOTOCONDUCTOR OVERCOATS COMPRISING RADICAL POLYMERIZABLE CHARGE TRANSPORT MOLECULES AND HEXA FUNCTIONAL URETHANE ACRYLATES”, which is assigned to the assignee of the present application and is incorporated by reference herein in its entirety. While this overcoat system improves paper edge wear versus crosslinkable silicon materials, a still greater improvement is needed and desired.
While a robust overcoat layer improves the life of photoconductor drums, a suitable overcoat layer is required that does not significantly alter the electrophotographic properties of the photoconductor drum. If the overcoat layer is too electrically insulating, the photoconductor drum will not discharge and will result in a poor latent image. On the other hand, if the overcoat layer is too electrically conducting, then the electrostatic latent image will spread resulting in a blurred image. Thus, a protective overcoat layer that improves life of the photoconductor drum must also allow charge migration to the photoconductor surface for development of the latent image with toner.